Imaging lens

ABSTRACT

There is provided an imaging lens with excellent optical characteristics which satisfies demand of wide field of view, low-profileness and low F-number in well balance. 
     An imaging lens comprises in order from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens having a concave surface facing the object side near an optical axis, a fifth lens, and a sixth lens having the concave surface facing the image side near the optical axis and negative refractive power, wherein said second lens has a convex surface facing the object side near the optical axis, composite refractive power of said second lens, said third lens and said fourth lens is negative, and below conditional expressions (1) and (2) are satisfied:
 
0.85&lt; vd 1/( vd 2+ vd 3)&lt;1.95   (1)
 
0.15&lt; vd 5/ vd 6&lt;0.55   (2)
 
where
     vd1: abbe number at d-ray of the first lens,   vd2: abbe number at d-ray of the second lens,   vd3: abbe number at d-ray of the third lens,   vd5: abbe number at d-ray of the fifth lens, and   vd6: abbe number at d-ray of the sixth lens.

The present application is based on and claims priority of a Japanesepatent application No. 2017-189361 filed on Sep. 29, 2017, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an imaging lens which forms an image ofan object on a solid-state image sensor such as a CCD sensor or a C-MOSsensor used in an imaging device, and more particularly to an imaginglens which is built in an imaging device mounted in an increasinglycompact and high-performance smartphone and mobile phone, an informationterminal such as a PDA (Personal Digital Assistant), a game console, PCand a robot, and moreover, a home appliance with camera function, amonitoring camera and an automobile.

Description of the Related Art

In recent years, it becomes common that camera function is mounted in ahome appliance, information terminal equipment, an automobile and publictransportation. Demand of products with the camera function is moreincreased, and development of products is being made accordingly.

The imaging lens mounted in such equipment is required to be compact andto have high-resolution performance. For Example, the following PatentDocument 1 and Patent Document 2 disclose the imaging lens comprisingsix lenses.

Patent Document 1 (JP2016-114803A) discloses an imaging lens comprising,in order from an object side, a first lens having a convex surfacefacing the object side and positive refractive power, a second lenshaving negative refractive power, a third lens having the convex surfacefacing the object side, a fourth lens having positive refractive power,a fifth lens having the negative refractive power, and a sixth lenshaving the negative refractive power.

Patent Document 2 (JP6085060B) discloses an imaging lens comprising, inorder from an object side, a first lens having the positive refractivepower, a second lens having the negative refractive power, a third lenshaving the negative refractive power, a fourth lens having the positiverefractive power, a fifth lens having the negative refractive power, anda sixth lens having the negative refractive power.

SUMMARY OF THE INVENTION

However, in lens configurations disclosed in the above-described PatentDocuments 1 and 2, when wide field of view, low-profileness and lowF-number are to be realized, it is very difficult to correct aberrationsat a peripheral area, and excellent optical performance can not beobtained.

The present invention has been made in view of the above-describedproblems, and an object of the present invention is to provide animaging lens with high resolution which satisfies demand of the widefield of view, the low-profileness and the low F-number in well balanceand excellently corrects aberrations.

Regarding terms used in the present invention, a convex surface, aconcave surface or a plane surface of lens surfaces implies that a shapeof the lens surface near an optical axis (paraxial portion), andrefractive power implies the refractive power near the optical axis. Thepole point implies an off-axial point on an aspheric surface at which atangential plane intersects the optical axis perpendicularly. The totaltrack length is defined as a distance along the optical axis from anobject-side surface of an optical element located closest to the objectto an image plane, when thickness of an IR cut filter or a cover glasswhich may be arranged between the imaging lens and the image plane isregarded as an air.

An imaging lens according to the present invention forms an image of anobject on a solid-state image sensor, and comprises in order from anobject side to an image side, a first lens, a second lens, a third lens,a fourth lens having a concave surface facing the object side near anoptical axis, a fifth lens and a sixth lens having the concave surfacefacing the image side near the optical axis and negative refractivepower.

The imaging lens having the above-described configuration achieves thewide field of view and the low-profileness by strengthening therefractive power of the first lens. The second lens properly correctsspherical aberration and chromatic aberration occurred at the firstlens. The third lens properly corrects coma aberration, astigmatism anddistortion. The fourth lens appropriately controls light ray incidentangle to the fourth lens by having the concave surface facing the objectside near the optical axis, and properly corrects the chromaticaberration and the astigmatism. The fifth lens properly corrects theastigmatism, field curvature and the distortion. The sixth lensmaintains the low-profileness and secures back focus by having theconcave surface facing the image side and the negative refractive power.Furthermore, the chromatic aberration, the distortion, the astigmatismand the field curvature are properly corrected.

According to the imaging lens having the above-described configuration,it is preferable that an object-side surface of the second lens has theconvex surface facing the object side near the optical axis.

When the object-side surface of the second lens is the convex surfacefacing the object side near the optical axis, the second lens properlycorrects the spherical aberration and the astigmatism.

According to the imaging lens having the above-described configuration,it is preferable that an object-side surface of the fifth lens is theconvex surface facing the object side near the optical axis.

When the object-side surface of the fifth lens is the convex surfacefacing the object side near the optical axis, the fifth lens properlycorrects the astigmatism and the field curvature.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (1) is satisfied:0.85<vd1/(vd2+vd3)<1.95   (1)where

vd1: abbe number at d-ray of the first lens,

vd2: abbe number at d-ray of the second lens, and

vd3: abbe number at d-ray of the third lens.

The conditional expression (1) defines relationship between the abbenumbers at d-ray of the first lens, the second lens and the third lens,and is a condition for properly correcting aberrations. By satisfyingthe conditional expression (1), the chromatic aberration is properlycorrected.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (2) is satisfied:0.15<vd5/vd6<0.55   (2)where

vd5: abbe number at d-ray of the fifth lens, and

vd6: abbe number at d-ray of the sixth lens.

The conditional expression (2) defines relationship between the abbenumbers at d-ray of the fifth lens and the sixth lens, and is acondition for properly correcting aberrations. By satisfying theconditional expression (2), the chromatic aberration is properlycorrected.

According to the imaging lens having the above-described configuration,it is preferable that the refractive power of the fourth lens ispositive, and more preferable that a below conditional expression (3) issatisfied:1.5<f4/f<4.0   (3)where

f4: focal length of the fourth lens, and

f: focal length of the overall optical system of the imaging lens.

When the refractive power of the fourth lens is positive, thelow-profileness becomes more facilitated. The conditional expression (3)defines the refractive power of the fourth lens, and is a condition forachieving the low-profileness and the proper aberration corrections.When a value is below the upper limit of the conditional expression (3),the positive refractive power of the fourth lens becomes appropriate andthe low-profileness becomes realizable. On the other hand, when thevalue is above the lower limit of the conditional expression (3), thespherical aberration and the coma aberration are properly corrected.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (4) is satisfied:0.1<T3/T4<0.5   (4)where

T3: distance along the optical axis from an image-side surface of thethird lens to an object-side surface of the fourth lens, and

T4: distance along the optical axis from an image-side surface of thefourth lens to the object-side surface of the fifth lens.

The conditional expression (4) defines a ratio of an interval betweenthe third lens and the fourth lens to an interval between the fourthlens and the fifth lens, and is a condition for achieving thelow-profileness and the proper aberration corrections. By satisfying theconditional expression (4), difference between the interval of the thirdlens and the fourth lens and the interval of the fourth lens and thefifth lens is suppressed from being increased, and the low-profilenessis achieved. Furthermore, by satisfying the conditional expression (4),the fourth lens is arranged at an optimum position, and aberrationcorrection function of the lens becomes more effective.

According to the imaging lens having the above-described configuration,it is preferable that composite refractive power of the third lens andthe fourth lens is positive, and more preferable that a belowconditional expression (5) is satisfied:1.3<f34/f<5.1   (5)where

f34: composite focal length of the third lens and the fourth lens, and

f: focal length of the overall optical system of the imaging lens.

When the composite refractive power of the third lens and the fourthlens is positive, the low-profileness becomes more facilitated. Theconditional expression (5) defines the composite refractive power of thethird lens and the fourth lens, and is a condition for achieving thelow-profileness and the proper aberration corrections. When a value isbelow the upper limit of the conditional expression (5), the positivecomposite refractive power of the third lens and the fourth lens becomesappropriate, and the low-profileness becomes realizable. On the otherhand, when the value is above the lower limit of the conditionalexpression (5), the astigmatism and the distortion are properlycorrected.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (6) is satisfied:0.10<f1/f4<0.55   (6)where

f1: focal length of the first lens, and

f4: focal length of the fourth lens.

The conditional expression (6) defines a ratio between the focal lengthof the first lens and the focal length of the fourth lens, and is acondition for achieving the low-profileness and the proper aberrationcorrections. When a value is below the upper limit of the conditionalexpression (6), the focal length of the fourth lens is suppressed frombeing too short, and position of Principal Point can be moved to theobject side. Therefore, the low-profileness becomes realizable.Furthermore, the field curvature and the distortion are properlycorrected. On the other hand, when the value is above the lower limit ofthe conditional expression (6), the focal length of the first lens issuppressed from being too short, and the spherical aberration and thecoma aberration are properly corrected.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (7) is satisfied:0.45<(D3/|f3|)×1000<8.00   (7)where

D3: thickness along the optical axis of the third lens, and

f3: focal length of the third lens.

The conditional expression (7) defines an appropriate range of thethickness along the optical axis of the third lens, and is a conditionfor properly maintaining formability of the third lens and achieving thelow-profileness. When a value is below the upper limit of theconditional expression (7), the thickness along the optical axis of thethird lens is suppressed from being too large, and an air gap of theobject side and the image side of the third lens can be easily secured.As a result, the low-profileness can be maintained. On the other hand,when the value is above the lower limit of the conditional expression(7), the thickness along the optical axis of the third lens issuppressed from being too small, and the formability of the lens becomesexcellent.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (8) is satisfied:5<(T4/TTL)×100<20   (8)where

T4: distance along the optical axis from an image-side surface of thefourth lens to an object-side surface of the fifth lens, and

TTL: total track length.

The conditional expression (8) defines the distance along the opticalaxis from the image-side surface of the fourth lens to the object-sidesurface of the fifth lens, and is a condition for achieving thelow-profileness and proper aberration corrections. By satisfying theconditional expression (8), the total track length can be shortened, andthe coma aberration, the field curvature and the distortion are properlycorrected.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (9) is satisfied:1.0<T4/T5<6.3   (9)where

T4: distance along the optical axis from the image-side surface of thefourth lens to the object-side surface of the fifth lens, and

T5: distance along the optical axis from the image-side surface of thefifth lens to an object-side surface of the sixth lens.

The conditional expression (9) defines a ratio of an interval betweenthe fourth lens and the fifth lens, and an interval between the fifthlens and the sixth lens, and is a condition for achieving thelow-profileness and the proper aberration corrections. By satisfying theconditional expression (9), difference between the interval of thefourth lens and the fifth lens and the interval of the fifth lens andthe sixth lens is suppressed from being large, and the low-profilenessis achieved. Furthermore, by satisfying the conditional expression (9),the fifth lens is arranged at an optimum position, and aberrationcorrection function of the lens becomes more effective.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (10) is satisfied:5.4<|f3|/f   (10)where

f3: focal length of the third lens, and

f: focal length of the overall optical system.

The conditional expression (10) defines the refractive power of thethird lens, and is a condition for achieving the low-profileness and theproper aberration corrections. When the value is above the lower limitof the conditional expression (10), the total track length is shortened,and the coma aberration and the astigmatism can be properly corrected.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (11) is satisfied:1.4<|f5|/f<32.0   (11)where

f5: focal length of the fifth lens, and

f: focal length of the overall optical system.

The conditional expression (11) defines the refractive power of thefifth lens, and is a condition for achieving the low-profileness and theproper aberration corrections. By satisfying the conditional expression(11), the total track length is shortened, and the chromatic aberration,the astigmatism, the field curvature and the distortion can be properlycorrected.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (12) is satisfied:−2.4<f6/f<−0.4   (12)where

f6: focal length of the sixth lens, and

f: focal length of the overall optical system.

The conditional expression (12) defines the refractive power of thesixth lens, and is a condition for achieving the low-profileness and theproper aberration corrections. When a value is below the upper limit ofthe conditional expression (12), negative refractive power of the sixthlens becomes appropriate, and the low-profileness can be achieved. Onthe other hand, when the value is above the lower limit of theconditional expression (12), the chromatic aberration, the fieldcurvature and the distortion can be properly corrected.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (13) is satisfied:Fno≤2.05   (13)where

Fno: F-number.

The conditional expression (13) defines the F-number. When a value isbelow the upper limit of the conditional expression (13), brightness canbe fully secured which is required for the imaging lens in recent years,if it is mounted in a portable mobile device, a digital camera, amonitoring camera, or an onboard camera.

According to the imaging lens having the above-described configuration,it is preferable that the second lens has a meniscus shape near theoptical axis.

When the second lens has the meniscus shape near the optical axis, thechromatic aberration, the spherical aberration, the coma aberration andthe field curvature are properly corrected.

According to the imaging lens having the above-described configuration,it is preferable that the fourth lens has a meniscus shape near theoptical axis.

When the fourth lens has the meniscus shape near the optical axis, thechromatic aberration, the spherical aberration and the distortion areproperly corrected.

According to the imaging lens having the above-described configuration,it is preferable that an image-side surface of the sixth lens is formedas an aspheric surface having an off-axial pole point.

When the image-side surface of the sixth lens has the off-axial polepoint, the field curvature and the distortion are properly corrected.

According to the imaging lens having the above-described configuration,it is preferable that a below conditional expression (14) is satisfied:−41.0<(1−N5)/(r10×f)×1000<0.8   (14)where

N5: refractive index at d-ray of the fifth lens,

r10: paraxial curvature radius of an image-side surface of the fifthlens, and

f: focal length of an overall optical system of the imaging lens.

The conditional expression (14) defines an appropriate range of therefractive power of the image-side surface of the fifth lens, and is acondition for properly correcting the aberrations and reducing thesensitivity to the manufacturing error. By satisfying the conditionalexpression (14), the refractive power of the image-side surface of thefifth lens becomes appropriate, and the spherical aberration occurred atthe fifth lens can be effectively suppressed and the sensitivity to themanufacturing error is effectively reduced.

According to the imaging lens having the above-described configuration,it is preferable that the refractive power of the first lens ispositive, and more preferable that a below conditional expression (15)is satisfied:0.35<f1/f<1.35   (15)where

f1: focal length of the first lens, and

f: focal length of the overall optical system of the imaging lens.

When the first lens has the positive refractive power, thelow-profileness is more facilitated. Furthermore, the conditionalexpression (15) defines the refractive power of the first lens, and is acondition for achieving the low-profileness and the proper aberrationcorrections. When a value is below the upper limit of the conditionalexpression (15), the positive refractive power of the first lens becomesappropriate, and the low-profileness can be achieved. On the other hand,when the value is above the lower limit of the conditional expression(15), the spherical aberration and the coma aberration are properlycorrected.

According to the imaging lens having the above-described configuration,it is preferable that the refractive power of the second lens isnegative, and more preferable that a below conditional expression (16)is satisfied:−4.7<f2/f<−0.8   (16)where

f2: focal length of the second lens, and

f: focal length of the overall optical system of the imaging lens.

When the second lens has the negative refractive power, the sphericalaberration and the chromatic aberration are properly corrected.Furthermore, the conditional expression (16) defines the refractivepower of the second lens, and is a condition for achieving thelow-profileness and the proper aberration corrections. When a value isbelow the upper limit of the conditional expression (16), the negativerefractive power of the second lens becomes appropriate, and thelow-profileness becomes realizable. On the other hand, when the value isabove the lower limit of the conditional expression (16), the chromaticaberration and the spherical aberration are properly corrected.

According to the imaging lens having the above-described configuration,it is preferable that composite refractive power of the first lens andthe second lens is positive, and more preferable that a belowconditional expression (17) is satisfied:0.5<f12/f<1.7   (17)where

f12: composite focal length of the first lens and the second lens, and

f: focal length of the overall optical system of the imaging lens.

When the composite refractive power of the first lens and the secondlens is positive, the low-profileness is more facilitated. Theconditional expression (17) defines the composite refractive power ofthe first lens and the second lens, and is a condition for achieving thelow-profileness and the proper aberration corrections. When a value isbelow the upper limit of the conditional expression (17), the positivecomposite refractive power of the first lens and the second lens becomesappropriate, and the low-profileness becomes realizable. On the otherhand, when the value is above the lower limit of the conditionalexpression (17), the spherical aberration and the coma aberration areproperly corrected.

According to the imaging lens having the above-described configuration,it is preferable that composite refractive power of the second lens, thethird lens and the fourth lens is negative, and more preferable that abelow conditional expression (18) is satisfied:f234/f<−2.65   (18)where

f234: composite focal length of the second lens, the third lens and thefourth lens, and

f: focal length of the overall optical system of the imaging lens.

When the composite refractive power of the second lens, the third lensand the fourth lens is negative, the chromatic aberration is properlycorrected. The conditional expression (18) defines composite refractivepower of the second lens, the third lens and the fourth lens, and is acondition for achieving the low-profileness and the proper aberrationcorrections. When a value is below the upper limit of the conditionalexpression (18), the negative composite refractive power of the secondlens, the third lens and the fourth lens becomes appropriate, and thelow-profileness becomes realizable. Furthermore, the sphericalaberration and the astigmatism are properly corrected.

Effect of Invention

According to the present invention, there can be provided an imaginglens with high resolution which satisfies, in well balance, demand ofthe wide field of view, the low-profileness and the low

F-number, and properly corrects aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a general configuration of an imaginglens in Example 1 according to the present invention;

FIG. 2 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 1 according to the present invention;

FIG. 3 is a schematic view showing the general configuration of animaging lens in Example 2 according to the present invention;

FIG. 4 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 2 according to the present invention;

FIG. 5 is a schematic view showing the general configuration of animaging lens in Example 3 according to the present invention;

FIG. 6 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 3 according to the present invention;

FIG. 7 is a schematic view showing the general configuration of animaging lens in Example 4 according to the present invention;

FIG. 8 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 4 according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the preferred embodiment of the present invention will bedescribed in detail referring to the accompanying drawings.

FIGS. 1, 3, 5 and 7 are schematic views of the imaging lenses inExamples 1 to 4 according to the embodiments of the present invention,respectively.

As shown in FIG. 1, the imaging lens according to the presentembodiments comprises in order from an object side to an image side, afirst lens L1, a second lens L2, a third lens L3, a fourth lens L4having a convex surface facing the object side near an optical axis X, afifth lens L5 and a sixth lens L6 having a concave surface facing theimage side near the optical axis X and negative refractive power.

A filter IR such as an IR cut filter and a cover glass is arrangedbetween the sixth lens L6 and an image plane IMG (namely, the imageplane of an image sensor). The filter IR is omissible.

By arranging an aperture stop ST in front of the first lens L1,correction of aberrations and control of the light ray incident angle ofhigh image height to the image sensor become facilitated.

The first lens L1 has the positive refractive power, and thelow-profileness is achieved by strengthening the positive refractivepower. The shape of the first lens L1 is a meniscus shape having theconvex surface facing the object side near the optical axis X, andspherical aberration and distortion are properly corrected.

The second lens L2 has the negative refractive power, and properlycorrects the spherical aberration and chromatic aberration occurring atthe first lens L1. A shape of the second lens L2 is the meniscus shapehaving the convex surface facing the object side near the optical axisX, and the chromatic aberration, the spherical aberration, astigmatism,coma aberration and field curvature are properly corrected.

The third lens L3 has the positive refractive power, and properlycorrects the coma aberration, the astigmatism and the distortion, whilemaintaining the low-profileness. A shape of the third lens L3 is abiconvex shape having convex surfaces facing the object side and theimage side near the optical axis X, and the low-profileness is achievedby the positive refractive power of the object-side and the image-sidesurfaces. Furthermore, the biconvex shape suppresses the curvature frombeing large, and effectively reduces the sensitivity to themanufacturing error. The refractive power of the third lens may benegative as in Examples 2, 3 and 4 shown in FIGS. 3, 5 and 7. In thiscase, the chromatic aberration is more properly corrected. A shape ofthe third lens may be the meniscus shape having the convex surfacefacing the object side near the optical axis X as in Examples 2, 3 and 4shown in FIGS. 3, 5 and 7. In this case, the astigmatism, the fieldcurvature and the distortion are more properly corrected.

The fourth lens L4 has the positive refractive power, and maintains thelow-profileness and properly corrects the spherical aberration and thechromatic aberration. A shape of the fourth lens L4 is the meniscusshape having the concave surface facing the object side near the opticalaxis X, therefore, light ray incident angle to the fourth lens L4 isappropriately controlled and the chromatic aberration, the sphericalaberration, distortion and the astigmatism are properly corrected.

The fifth lens L5 has the positive refractive power, and theastigmatism, the field curvature and the distortion are properlycorrected. A shape of the fifth lens L5 is a meniscus shape having theconvex surface facing the object side near the optical axis X, thereforethe coma aberration, the astigmatism, the field curvature and thedistortion are properly corrected. The refractive power of the fifthlens L5 may be negative as in Example 4 shown in FIG. 7. In this case,the chromatic aberration is properly corrected. Furthermore, the shapeof the fifth lens L5 may be a biconvex shape having the convex surfacesfacing the object side and the image side near the optical axis X as inExample 2 shown in FIG. 3. In this case, the low-profileness is morefacilitated by the positive refractive power of the object-side surfaceand the image-side surface. Furthermore, the biconvex shape has aneffect to suppress curvature from being large, and to reduce thesensitivity to the manufacturing error.

The sixth lens L6 has the negative refractive power, and maintains thelow-profileness and secures back focus. A shape of the sixth lens L6 isa meniscus shape having the concave surface facing the image side nearthe optical axis X, therefore both of the low-profileness and thesecuring the back focus are realized at the same time. Furthermore, thechromatic aberration, the distortion, the astigmatism and the fieldcurvature are properly corrected. In addition, an image-side surface ofthe sixth lens L6 has an off-axial pole point and the field curvatureand the distortion are properly corrected.

Regarding the imaging lens according to the present embodiments, alllenses are single lenses. Configuration without cemented lenses canfrequently use the aspheric surfaces, and proper correction of theaberrations can be facilitated. Furthermore, workload for cementing isnot required, and manufacturing in low cost becomes realizable.

Regarding the imaging lens according to the present embodiments, aplastic material is used for all of the lenses, and manufacturing isfacilitated and mass production in a low cost can be realized. Both-sidesurfaces of all lenses are appropriate aspheric, and the aberrations arefavorably corrected.

The material applied to the lens is not limited to the plastic material.By using glass material, further high performance may be aimed. It ispreferable that all of surfaces of lenses are formed as asphericsurfaces, however, spherical surfaces easy to manufacture may be adoptedin accordance with required performance.

The imaging lens according to the present embodiments shows preferableeffect by satisfying the below conditional expressions (1) to (18).0.85<vd1/(vd2+vd3)<1.95   (1)0.15<vd5/vd6<0.55  (2)1.5<f4/f<4.0   (3)0.1<T3/T4<0.5   (4)1.3<f34/f<5.1   (5)0.10<f1/f4<0.55   (6)0.45<(D3/|f3|)×1000<8.00   (7)5<(T4/TTL)×100<20   (8)1.0<T4/T5<6.3   (9)5.4<|f3|/f   (10)1.4<|f5|/f<32.0   (11)−2.4<f6/f<−0.4   (12)Fno≤2.05   (13)−41.0<(1−N5)/(r10×f)×1000<0.8   (14)0.35<f1/f<1.35   (15)−4.7<f2/f<−0.8   (16)0.5<f12/f<1.7   (17)f234/f<−2.65   (18)where

vd1: abbe number at d-ray of the first lens L1,

vd2: abbe number at d-ray of the second lens L2,

vd3: abbe number at d-ray of the third lens L3,

vd5: abbe number at d-ray of the fifth lens L5,

vd6: abbe number at d-ray of the sixth lens L6,

D3: thickness along the optical axis X of the third lens L3,

T3: distance along the optical axis X from an image-side surface of thethird lens to an object-side surface of the fourth lens L4,

T4: distance along the optical axis X from an image-side surface of thefourth lens L4 to the object-side surface of the fifth lens L5,

T5: distance along the optical axis X from the image-side surface of thefifth lens L5 to an object-side surface of the sixth lens L6,

N5: refractive index at d-ray of the fifth lens L5,

TTL: total track length,

f: focal length of the overall optical system of the imaging lens,

f1: focal length of the first lens L1,

f2: focal length of the second lens L2,

f3: focal length of the third lens L3,

f4: focal length of the fourth lens L4,

f5: focal length of the fifth lens L5,

f6: focal length of the sixth lens L6,

f12: composite focal length of the first lens L1 and the second lens L2,

f34: composite focal length of the third lens and the fourth lens L4,

f234: composite focal length of the second lens L2, the third lens andthe fourth lens L4,

r10: paraxial curvature radius of an image-side surface of the fifthlens L5,

Fno: F-number.

It is not necessary to satisfy the above all conditional expressions,and by satisfying the conditional expression individually, operationaladvantage corresponding to each conditional expression can be obtained.

The imaging lens according to the present embodiments shows furtherpreferable effect by satisfying the below conditional expressions (1a)to (18a).1.10<vd1/(vd2+vd3)<1.65   (1a)0.27<vd5/vd6<0.46   (2a)2.0<f4/f<3.6   (3a)0.2<T3/T4<0.4   (4a)2.0<f34/f<4.2   (5a)0.17<f1/f4<0.43   (6a)0.75<(D3/|f3|)×1000<6.40   (7a)7<(T4/TTL)×100<17   (8a)1.35<T4/T5<5.20   (9a)8.1<|f3|/f   (10a)2.1<|f5|/f<27.0   (11a)−2.0<f6/f<−0.6   (12a)Fno≤1.95   (13a)−34.0<(1−N5)/(r10×f)×1000<0.7   (14a)0.53<f1/f<1.10   (15a)−3.9<f2/f<−1.2   (16a)0.8<f12/f<1.40   (17a)f234/f<−4.00   (18a)

The signs in the above conditional expressions have the same meanings asthose in the paragraph before the preceding paragraph.

In this embodiment, the aspheric shapes of the surfaces of the asphericlens are expressed by Equation 1, where Z denotes an axis in the opticalaxis direction, H denotes a height perpendicular to the optical axis, Rdenotes a paraxial curvature radius, k denotes a conic constant, and A4,A6, A8, A10, Al2, A14, A16, A18 and A20 denote aspheric surfacecoefficients.

Equation 1,

$Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}} + {A_{18}H^{18}} + {A_{20}H^{20}}}$

Next, examples of the imaging lens according to this embodiment will beexplained. In each example, f denotes the focal length of the overalloptical system of the imaging lens, Fno denotes an F-number, ω denotes ahalf field of view, ih denotes a maximum image height, and TTL denotes atotal track length. Additionally, i denotes surface number counted fromthe object side, r denotes a curvature radius, d denotes the distance oflenses along the optical axis (surface distance), Nd denotes arefractive index at d-ray (reference wavelength), and vd denotes an abbenumber at d-ray. As for aspheric surfaces, an asterisk (*) is addedafter surface number i.

EXAMPLE 1

The basic lens data is shown below in Table 1.

TABLE 1 Example 1 Unit mm f = 5.57 Fno = 1.85 ω(°) = 38.9 ih = 4.60 TTL= 6.14 Surface Data Surface Curvature Surface Refractive Abbe Number iRadius r Distance d Index Nd Number vd (Object) Infinity Infinity  1(Stop) Infinity −0.6950   2* 1.8498 0.8998 1.544 55.86 (vd1)  3* 11.51840.0640  4* 12.2479 0.2720 1.661 20.37 (vd2)  5* 3.9710 0.5502  6*154.0651 0.3140 1.661 20.37 (vd3)  7* −199.7972 0.1754  8* −4.89590.6914 1.535 55.66 (vd4)  9* −3.3581 0.5903 10* 11.6768 0.5199 1.66120.37 (vd5) 11* 36.9238 0.3510 12* 14.2736 0.5696 1.535 55.66 (vd6) 13*2.2692 0.1290 14 Infinity 0.1100 1.515 57.00 15 Infinity 0.9450 ImagePlane Infinity Constituent Lens Data Lens Start Surface Focal LengthComposite Focal Length 1 2 3.920 f12 5.817 2 4 −9.011 f34 15.436 3 6131.697 f234 −30.821 4 8 17.284 5 10 25.635 6 12 −5.130 Aspheric SurfaceData Second Surface Third Surface Fourth Surface Fifth Surface SixthSurface Seventh Surface k 0.000000E+00 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00  0.000000E+00 A4 −6.559581E−04  2.559000E−022.284504E−02 2.682232E−02 −4.172539E−02   −3.027155E−02 A6 6.442845E−03−9.383953E−02  −5.529928E−02  −4.032163E−04  −8.424975E−02  −8.717156E−02 A8 −4.408570E−03  1.662446E−01 1.047506E−01 2.178822E−021.023932E−01  1.018458E−01 A10 1.764813E−03 −1.593960E−01 −9.850767E−02  −3.805573E−02  −6.369973E−02   −6.930064E−02 A12−3.511485E−04  8.605984E−02 5.226970E−02 6.428401E−02 −1.820655E−02   2.755993E−02 A14 2.509990E−04 −2.443979E−02  −1.411061E−02 −5.239218E−02  4.003634E−02 −3.313245E−03 A16 −9.457196E−05 2.829188E−03 1.565588E−03 1.777256E−02 −1.210243E−02   −3.868398E−04 A180.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 A20 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+000.000000E+00  0.000000E+00 Eighth Surface Ninth Surface Tenth SurfaceEleventh Surface Twelfth Surface Thirteenth Surface k 0.000000E+00−4.400000E+00  0.000000E+00 0.000000E+00 0.000000E+00 −1.130349E+01 A41.039403E−02 −1.505980E−02  3.853971E−02 7.933503E−02 −1.001545E−01  −6.446041E−02 A6 −5.509970E−02  −3.348522E−02  −9.895048E−02 −1.122584E−01  2.612098E−02  1.846708E−02 A8 4.845284E−02 4.159510E−026.227574E−02 6.251712E−02 −3.505904E−03   −2.627240E−03 A10 1.374759E−02−1.551296E−02  −2.326417E−02  −2.130620E−02  2.777474E−04 −4.185365E−05A12 −3.091849E−02  2.268646E−03 5.700107E−03 4.797404E−03−1.172069E−05    7.376613E−05 A14 1.541680E−02 1.066620E−05−9.581516E−04  −7.250518E−04  1.105851E−07 −1.159327E−05 A16−3.733299E−03  −3.852843E−05  1.025728E−04 7.094787E−05 9.585782E−09 8.743948E−07 A18 4.560274E−04 3.398593E−06 −5.286202E−06 −4.042592E−06  −2.620563E−10   −3.335456E−08 A20 −2.251891E−05 −6.292081E−08  3.802779E−08 1.012336E−07 −2.121172E−13    5.148077E−10

The imaging lens in Example 1 satisfies conditional expressions (1) to(18) as shown in Table 5.

FIG. 2 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 1. The spherical aberration diagramshows the amount of aberration at wavelengths of F-ray (486 nm), d-ray(588 nm), and C-ray (656 nm). The astigmatism diagram shows the amountof aberration at d-ray on a sagittal image surface S (solid line) and ontangential image surface T (broken line), respectively (same as FIGS. 4,6 and 8).

EXAMPLE 2

The basic lens data is shown below in Table 2.

TABLE 2 Example 2 Unit mm f = 5.55 Fno = 1.85 ω(°) = 38.9 ih = 4.60 TTL= 6.11 Surface Data Surface Curvature Surface Refractive Abbe Number iRadius r Distance d Index Nd Number vd (Object) Infinity Infinity  1(Stop) Infinity −0.7400   2* 1.8572 0.9359 1.544 55.86 (vd1)  3* 11.34040.0734  4* 14.5777 0.2720 1.661 20.37 (vd2)  5* 4.2204 0.5225  6*39.0415 0.3116 1.661 20.37 (vd3)  7* 32.9021 0.1970  8* −6.3976 0.67831.535 55.66 (vd4)  9* −3.6048 0.6462 10* 12.0963 0.5529 1.661 20.37(vd5) 11* −216.4456 0.2580 12* 87.1604 0.5010 1.535 55.66 (vd6) 13*2.4060 0.2065 14 Infinity 0.2100 1.517 64.20 15 Infinity 0.8163 ImagePlane Infinity Constituent Lens Data Lens Start Surface Focal LengthComposite Focal Length 1 2 3.943 f12 5.826 2 4 −9.085 f34 14.887 3 6−323.184 f234 −33.643 4 8 14.236 5 10 17.355 6 12 −4.636 AsphericSurface Data Second Surface Third Surface Fourth Surface Fifth SurfaceSixth Surface Seventh Surface k 0.000000E+00 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00  0.000000E+00 A4 −6.342804E−04  2.234428E−022.306549E−02 2.963554E−02 −4.669113E−02  −4.093846E−02 A6 5.655337E−03−8.538420E−02  −5.177875E−02  −4.176486E−03  −7.192142E−02 −7.578732E−02 A8 −4.022756E−03  1.555427E−01 1.003881E−01 2.612834E−028.530819E−02  8.769303E−02 A10 1.821660E−03 −1.504253E−01 −9.445740E−02  −3.889139E−02  −4.179403E−02  −5.498314E−02 A12−2.846371E−04  8.180085E−02 4.971829E−02 6.084507E−02 −3.349007E−02  1.815010E−02 A14 6.266105E−05 −2.341677E−02  −1.335419E−02 −4.914423E−02  4.412678E−02 −1.807224E−04 A16 −1.876379E−05 2.741503E−03 1.450510E−03 1.649142E−02 −1.227326E−02  −7.805473E−04 A180.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 A20 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+000.000000E+00  0.000000E+00 Eighth Surface Ninth Surface Tenth SurfaceEleventh Surface Twelfth Surface Thirteenth Surface k 0.000000E+00−4.700000E+00  0.000000E+00 0.000000E+00 0.000000E+00 −1.240285E+01 A4−1.828260E−02  −4.687316E−02  −6.569252E−03  5.398080E−02 −8.474884E−02 −6.365190E−02 A6 −9.335539E−03  2.167643E−02 −4.703180E−02 −7.841651E−02  2.141104E−02  1.959963E−02 A8 −3.486233E−02 −2.858853E−02  1.882355E−02 3.503142E−02 −2.663913E−03  −2.894987E−03A10 9.957474E−02 3.852318E−02 −1.137796E−03  −8.494981E−03  1.937787E−04−6.218703E−05 A12 −8.176753E−02  −2.225627E−02  −7.060111E−04 1.260978E−03 −7.590533E−06   8.797136E−05 A14 3.352026E−02 6.689786E−031.442286E−05 −1.309689E−04  6.645372E−08 −1.376079E−05 A16−7.581506E−03  −1.116383E−03  5.237772E−05 1.114399E−05 5.471120E−09 1.038188E−06 A18 9.076717E−04 9.860436E−05 −9.490414E−06 −7.225287E−07  −1.113657E−10  −3.974873E−08 A20 −4.508993E−05 −3.609409E−06  5.011811E−07 2.301853E−08 −1.480635E−12   6.182129E−10

The imaging lens in Example 2 satisfies conditional expressions (1) to(18) as shown in Table 5.

FIG. 4 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 2.

EXAMPLE 3

The basic lens data is shown below in Table 3.

TABLE 3 Example 3 Unit mm f = 5.56 Fno = 1.85 ω(°) = 38.9 ih = 4.60 TTL= 6.11 Surface Data Surface Curvature Surface Refractive Abbe Number iRadius r Distance d Index Nd Number vd (Object) Infinity Infinity  1(Stop) Infinity −0.7000   2* 1.8455 0.8971 1.544 55.86 (vd1)  3* 10.81830.0768  4* 13.4155 0.2720 1.661 20.37 (vd2)  5* 4.1391 0.5373  6*37.3848 0.3132 1.661 20.37 (vd3)  7* 27.8952 0.1923  8* −6.2573 0.66061.535 55.66 (vd4)  9* −3.6041 0.6714 10* 10.2553 0.5600 1.661 20.37(vd5) 11* 359.8995 0.2360 12* 38.8894 0.5029 1.535 55.66 (vd6) 13*2.3210 0.7677 14 Infinity 0.2100 1.517 64.20 15 Infinity 0.2838 ImagePlane Infinity Constituent Lens Data Lens Start Surface Focal LengthComposite Focal Length 1 2 3.949 f12 5.828 2 4 −9.166 f34 15.956 3 6−168.531 f234 −29.504 4 8 14.624 5 10 15.966 6 12 −4.638 AsphericSurface Data Second Surface Third Surface Fourth Surface Fifth SurfaceSixth Surface Seventh Surface k 0.000000E+00 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00  0.000000E+00 A4 −4.946121E−04  2.267080E−022.353818E−02 3.022076E−02 −4.770152E−02  −4.202540E−02 A6 5.786111E−03−8.749157E−02  −5.306485E−02  −4.406100E−03  −7.447459E−02 −7.802990E−02 A8 −4.149531E−03  1.610588E−01 1.040789E−01 2.695961E−028.800908E−02  .080999E−02 A10 1.929501E−03 −1.573373E−01  −9.874235E−02 −4.023377E−02  −4.356354E−02  −5.752268E−02 A12 −2.961480E−04 8.642653E−02 5.254263E−02 6.427705E−02 −3.543918E−02   1.912507E−02 A146.614429E−05 −2.498795E−02  −1.424717E−02  −5.243613E−02  4.708012E−02−2.129969E−04 A16 −2.468631E−05  2.952803E−03 1.563187E−03 1.777252E−02−1.320184E−02  −8.224367E−04 A18 0.000000E+00 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00  0.000000E+00 A20 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00 0.000000E+00  0.000000E+00 Eighth SurfaceNinth Surface Tenth Surface Eleventh Surface Twelfth Surface ThirteenthSurface k 0.000000E+00 −4.600000E+00  0.000000E+00 0.000000E+000.000000E+00 −1.247092E+01 A4 −1.748117E−02  −4.754487E−02 −2.811301E−03  6.393265E−02 −8.704856E−02  −6.468958E−02 A6−1.648781E−02  2.162668E−02 −4.769532E−02  −8.756304E−02  2.196503E−02 2.013024E−02 A8 −2.216618E−02  −2.887865E−02  1.665962E−02 4.030752E−02−2.756181E−03  −2.998648E−03 A10 9.115253E−02 4.078847E−02 1.827636E−03−1.049712E−02  2.027897E−04 −6.512143E−05 A12 −7.928899E−02 −2.425107E−02  −2.679381E−03  1.740165E−03 −8.016603E−06   9.292714E−05A14 3.333797E−02 7.445778E−03 7.527842E−04 −1.999273E−04  7.067856E−08−1.468296E−05 A16 −7.644853E−03  −1.260980E−03  −1.032320E−04 1.664855E−05 5.850558E−09  1.118834E−06 A18 9.210592E−04 1.122233E−047.637359E−06 −9.240680E−07  −1.249598E−10  −4.326534E−08 A20−4.574249E−05  −4.106910E−06  −2.617430E−07  2.464162E−08 −1.479305E−12  6.799722E−10

The imaging lens in Example 3 satisfies conditional expressions (1) to(18) as shown in Table 5.

FIG. 6 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 3.

EXAMPLE 4

The basic lens data is shown below in Table 4.

TABLE 4 Example 4 Unit mm f = 5.57 Fno = 1.85 ω(°) = 39.0 ih = 4.60 TTL= 6.12 Surface Data Surface Curvature Surface Refractive Abbe Number iRadius r Distance d Index Nd Number vd (Object) Infinity Infinity  1(Stop) Infinity −0.6864   2* 1.8569 0.9100 1.544 55.86 (vd1)  3* 5.00490.0603  4* 5.1448 0.2720 1.661 20.37 (vd2)  5* 3.4735 0.4625  6* 8.30240.3100 1.661 20.37 (vd3)  7* 6.7689 0.2203  8* −10.0238 0.6302 1.53555.66 (vd4)  9* −4.4430 0.8128 10* 4.8191 0.5500 1.661 20.37 (vd5) 11*4.3335 0.1947 12* 3.6522 0.5010 1.535 55.66 (vd6) 13* 1.9622 0.4000 14Infinity 0.2100 1.517 64.20 15 Infinity 0.6567 Image Plane InfinityConstituent Lens Data Lens Start Surface Focal Length Composite FocalLength 1 2 4.922 f12 6.158 2 4 −17.302 f34 18.827 3 6 −60.312 f234−1151.202 4 8 14.356 5 10 −118.482 6 12 −8.842 Aspheric Surface DataSecond Surface Third Surface Fourth Surface Fifth Surface Sixth SurfaceSeventh Surface k 0.000000E+00  0.000000E+00 0.000000E+00 0.000000E+000.000000E+00  0.000000E+00 A4 −9.111594E−03  −1.375849E−01−1.594074E−01  −7.325244E−02  −9.922091E−02  −9.510008E−02 A64.390541E−02  1.861026E−01 2.243824E−01 3.004185E−01 1.650987E−01 6.241214E−02 A8 −1.180540E−01  −2.227964E−01 −1.887395E−01 −8.856036E−01  −6.422379E−01  −1.284175E−01 A10 2.000953E−01 2.776258E−01 1.578480E−01 2.136778E+00 1.595913E+00  2.124838E−01 A12−2.130619E−01  −2.788869E−01 −1.409545E−01  −3.415915E+00 −2.533675E+00  −2.472751E−01 A14 1.422831E−01  1.868630E−01 1.028481E−013.486739E+00 2.543245E+00  1.877763E−01 A16 −5.789803E−02  −7.704877E−02−4.896303E−02  −2.181214E+00  −1.570309E+00  −8.583508E−02 A181.314307E−02  1.767026E−02 1.325383E−02 7.619823E−01 5.459317E−01 2.172014E−02 A20 −1.286694E−03  −1.731680E−03 −1.546597E−03 −1.132203E−01  −8.174229E−02  −2.371466E−03 Eighth Surface Ninth SurfaceTenth Surface Eleventh Surface Twelfth Surface Thirteenth Surface k0.000000E+00 −6.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00−1.058352E+01 A4 −6.188089E−02  −6.111057E−02 −4.790255E−02 −9.157841E−02  −2.910210E−01  −1.090455E−01 A6 −1.376293E−02 −1.737701E−03 −2.110406E−02  3.635774E−02 1.704165E−01  5.449575E−02 A89.993203E−02  4.210796E−02 2.778180E−02 −1.920033E−02  −6.164386E−02 −1.594843E−02 A10 −1.776434E−01  −5.357525E−02 −2.745452E−02 6.152359E−03 1.424323E−02  2.946430E−03 A12 1.841311E−01  4.314689E−021.630409E−02 −8.422575E−04  −2.130098E−03  −3.658126E−04 A14−1.049806E−01  −1.992599E−02 −5.460821E−03  −2.881454E−05  2.059452E−04 3.089347E−05 A16 3.276377E−02  5.121228E−03 1.023742E−03 2.266185E−05−1.247888E−05  −1.704859E−06 A18 −5.282316E−03  −6.904365E−04−1.003743E−04  −2.477601E−06  4.323906E−07  5.518661E−08 A203.450721E−04  3.841306E−05 4.007943E−06 8.927946E−08 −6.557250E−09 −7.898252E−10

The imaging lens in Example 4 satisfies conditional expressions (1) to(18) as shown in Table 5.

FIG. 8 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 4.

In table 5, values of conditional expressions (1) to (18) related to theExamples 1 to 4 are shown.

TABLE 5 Conditional expression Example1 Example2 Example3 Example4 (1)vd1/(vd2 + vd3) 1.37 1.37 1.37 1.37 (2) vd5/vd6 0.37 0.37 0.37 0.37 (3)f4/f 3.11 2.56 2.63 2.58 (4) T3/T4 0.30 0.30 0.29 0.27 (5) f34/f 2.772.68 2.87 3.38 (6) f1/f4 0.23 0.28 0.27 0.34 (7) (D3/|f3|) × 1000 2.380.96 1.86 5.14 (8) (T4/TTL) × 100 9.61 10.58 10.99 13.28 (9) T4/T5 1.682.50 2.84 4.17 (10)  |f3|/f 23.66 58.21 30.30 10.83 (11)  |f5|/f 4.613.13 2.87 21.27 (12)  f6/f −0.92 −0.84 −0.83 −1.59 (13)  Fno 1.85 1.851.85 1.85 (14)  (1 − N5)/ −3.22 0.55 −0.33 −27.37 (r10 × f) × 1000 (15) f1/f 0.70 0.71 0.71 0.88 (16)  f2/f −1.62 −1.64 −1.65 −3.11 (17)  f12/f1.05 1.05 1.05 1.11 (18)  f234/f −5.54 −6.06 −5.30 −206.68

When the imaging lens according to the present invention is adopted to aproduct with the camera function, contribution is made to the wide fieldof view, the low-profileness and the low F-number of the camera and alsoto high performance thereof.

DESCRIPTION OF REFERENCE NUMERALS

ST: aperture stop

L1: first lens

L2: second lens

L3: third lens

L4: fourth lens

L5: fifth lens

L6: sixth lens

ih: maximum image height

IR: filter

IMG: image plane

What is claimed is:
 1. An imaging lens comprising in order from anobject side to an image side, a first lens, which has a meniscus shapenear an optical axis, a second lens, which has a meniscus shape near theoptical axis, a third lens, a fourth lens, which has a meniscus shapenear the optical axis, a fifth lens, and a sixth lens, which has ameniscus shape near the optical axis, wherein below conditionalexpressions (1), (2) and (4a) are satisfied:0.85<vd1/(vd2+vd3)<1.95   (1)0.15<vd5/vd6<0.55   (2)0.2<T3/T4<0.4   (4a) where vd1: abbe number at d-ray of the first lens,vd2: abbe number at d-ray of the second lens, vd3: abbe number at d-rayof the third lens, vd5: abbe number at d-ray of the fifth lens, vd6:abbe number at d-ray of the sixth lens, T3: distance along the opticalaxis from an image-side surface of the third lens to an object-sidesurface of the fourth lens, and T4: distance along the optical axis froman image-side surface of the fourth lens to an object-side surface ofthe fifth lens.
 2. The imaging lens according to claim 1, wherein abelow conditional expression (3) is satisfied:1.5<f4/f<4.0   (3) where f4: focal length of the fourth lens, and f:focal length of the overall optical system of the imaging lens.
 3. Theimaging lens according to claim 1, wherein a below conditionalexpression (5) is satisfied:1.3<f34/f<5.1   (5) where f34: composite focal length of the third lensand the fourth lens, and f: focal length of the overall optical systemof the imaging lens.
 4. The imaging lens according to claim 1, wherein abelow conditional expression (6) is satisfied:0.10<f1/f4<0.55   (6) where f1: focal length of the first lens, and f4:focal length of the fourth lens.
 5. The imaging lens according to claim1, wherein a below conditional expression (7) is satisfied:0.45<(D3/|f3|)×1000<8.00   (7) where 03: thickness along the opticalaxis of the third lens, and f3: focal length of the third lens.
 6. Theimaging lens according to claim 1, wherein a below conditionalexpression (8) is satisfied:5<(T4/TTL)×100<20   (8) where T4: distance along the optical axis fromthe image-side surface of the fourth lens to the object-side surface ofthe fifth lens, and TIL: total track length.
 7. The imaging lensaccording to claim 1, wherein a below conditional expression (9) issatisfied:1.0<T4/T5<6.3   (9) where T4: distance along the optical axis from theimage-side surface of the fourth lens to the object-side surface of thefifth lens, and T5: distance along the optical axis from an image-sidesurface of the fifth lens to an object-side surface of the sixth lens.8. The imaging lens according to claim 1, wherein a below conditionalexpression (10) is satisfied:5.4<|f3|/f   (10) where f3: focal length of the third lens, and f: focallength of the overall optical system of the imaging lens.
 9. The imaginglens according to claim 1, wherein a below conditional expression (11)is satisfied:1.4<|f5|/f<32.0   (11) where f5: focal length of the fifth lens, and f:focal length of the overall optical system of the imaging lens.
 10. Theimaging lens according to claim 1, wherein a below conditionalexpression (12) is satisfied:−2.4<f6/f<−0.4   (12) where f6: focal length of the sixth lens, and f:focal length of the overall optical system of the imaging lens.
 11. Theimaging lens according to claim 1, wherein a below conditionalexpression (13) is satisfied:Fno<=2.05   (13) where Fno: F-number.